Not applicable
1. Field of the Invention
The present invention relates to spin valves. More particularly, the present invention relates to spin valves having good switching characteristics and a strong anisotropy in these characteristics.
2. General Background of the Invention
Current readily available commercial field sensors rely mainly on two types of technologies and materials, neither of which is desirable in overall performance, material usage and economical considerations. The first type is the flux gate technology that incorporates complicated electronics with specific structures made of soft magnetic materials. The flux gate sensors are bulky, power demanding, and very costly. Especially, when the need arises to measure three dimensional field distribution three independent flux gate gages are required to carry out the job, further increasing the cost and power consumption.
The second type of sensors is the so-called Hall sensor. The conventional Hall sensors use the Hall voltage induced by a magnetic field in semiconductor system to probe the local magnetic fields. Most of them are doped semiconductors with controlled impurity densities to achieve required sensitivity. The main problem is that the sensitivity is generally sacrificed by temperature instability, which for doped semiconductors is quite poor due to the exponential dependence of carrier density with temperature. Also, the sensitivity of the Hall sensors is not as high.
A good background discussion of spin valves can be found in U.S. Pat. No. 5,919,580.
The following U.S. Patents are incorporated herein by reference:
Pat. No. Title
1. U.S. Pat. No. 6,031,692, Magentoresistive deice and magnetoresistive head
2. U.S. Pat. No. 6,013,365, Multi-layer structure and sensor and manufacturing process
3. U.S. Pat. No. 5,993,566, Fabrication process of Ni-Mn spin valve sensor
4. U.S. Pat. No. 5,948,553, Magnetic multiplayer structure having magnetoresistance ration and large magnetic sensitivity base on the giant magnetoresistance effect and process of fabrication thereof
5. U.S. Pat. No. 5,942,309, Spin valve magnetoresistive device
6. U.S. Pat. No. 5,919,580, Spin valve device containing a Cr-rich antiferromagnetic pinning layer
7. U.S. Pat. No. 5,909,345, Magnetoresistive device and magnetoresistive head
8. U.S. Pat. No. 5,871,622, Method for making a spin valve magnetoresistive sensor
9. U.S. Pat. No. 5,843,589, Magnetic layered material, and magnetic sensor and magnetic storage/read system based theron
10. U.S. Pat. No. 5,701,222, Spin valve sensor with antiparallel magnetization of pinned layers
11. U.S. Pat. No. 5,648,885, Gaint magnetoresistive eeffect sensor, particularly having a multilayered magnetic thin film layer
12. U.S. Pat. No. 5,514,452, Magnetic multiplayer film and magnetoresistance element
An article entitled xe2x80x9cQuantum size effect and magnetoresistance in spin-valved Co/Cu/Co trilayer structuresxe2x80x9d by Z. T. Diao, S. Tsunashima and M. Jimbo, in the J. Appl. Phys. vol. 85 no.3 pp. 1679-88, 1999 discusses electron transport and the magnetoresistance of magnetron sputtered ultrathin Co(M1)/Cu/Co(M2) trilayer structures. These properties are presented as a function of magnetic and nonmagnetic layer thicknesses on 5 nm Fe layer; a quantum well states model is applied to interpret the electron transport data; this approach represents a beyond free-electron approximation that takes into model calculations details of the electronic band structure of the trilayers and spin-dependent scattering by impurities and/or at interfaces. The article is limited to model treatment of magneto-electron transport properties and are not concerned with good magnetic switching characteristics and field sensitivity. In fact as presented in FIG. 1 of the article the low field magnetoresistance switching characteristics are rather poor.
The apparatus of the present invention solves the problems confronted in the art in a simple and straightforward manner. What is provided are spin valves having good switching characteristics and a method of producing the spin valves.
Uniaxial magnetic anisotropy is found in the Fe Co Cu Co magnetoresistive structures deposited on Si (100) substrates. Samples show extremely sharp magnetization and magnetoresistance switching at low fields along an easy anisotropy axis, with large value of giant magnetoresistance effect (e.g. 9.5% at cryogenic temperatures and 5.5% at room temperature). The samples consist of a Fe buffer, a thicker lower Co layer, a thin Cu spacer and a thin upper Co layer. Also, a thin capping layer of either Cu or Cr may be used. These samples are advantageous compared to other spin valves on nonmagentic buffer layer and do not exhibit strong uniaxial anisotropy. The samples are made in a magnetron sputtering high vacuum deposition system. The strong magnetic anisotropy is induced by applying a magnetic field during the deposition process. It is especially important to use a magnetic. seed layer in the magnetic field to produce textured structure with the desirable anisotropy. A magnetic field is produced by a magnet or a current coil placed in the vicinity of the wafer or substrate on which the spin valve films are to be deposited during the deposition process. The magnetic field is to help textured growth of the magnetic seed layer and the subsequent magnetic layers. The good textured growth of non-magnetic layers also follows.
Magnetic field sensors are extensively used in various applications ranging from electronic compass, motion sensors, positioning sensors, magnetic recording head, to nonvolatile random access memory, and light weight magnetometer, to name a few. The existing difficulties with the current field sensor technologies, of low sensitivity, heavy weight, high power consumption, low stability and high cost, can be overcome by these newly discovered field sensitive materials such as the spin valve materials. These sensors provide a solid-state solution for small size, low cost, low power, and microelectronic ready field sensors. Especially directional sensing capability in the current invention is a new feature that can be used to determine the Earth""s magnetic field, determine the orientation of a vehicle in space or on the ocean""s surface, and determine large ferrous objects such as automobiles, ship and airplane by detecting the disturbances of the Earth""s magnetic field. They can also be used in buoys to detect tidal waves by detecting the direction and height variation of the buoy. In microelectronic and memory chip technologies they can be used to simplify the circuit construction improve the modes of bit operations, lower the manufacturing costs, and improve the performance characteristics.